Thermally feedable transmitter and sensor system

ABSTRACT

The transmitter which can be fed thermally has at least one heat transducer element ( 1 ) with a downstream voltage transformer ( 3 ) and logic assembly ( 4 ) as well as a data transmission unit ( 5, 6 ), and is characterized in that the logic assembly ( 4 ) is designed on a ULP basis, and the data transmission unit ( 5, 6 ) transmits a broadband signal.

[0001] The invention relates to a transmitter which is fed thermally, toits use, to a method for thermally fed transmission of a signal, inparticular of a radio signal, and to a system for monitoring and/orcontrol.

[0002] By way of example, DE 36 43 236 C2 discloses systems in whichmechanical energy is converted to electrical energy, and is thenrectified. This electrical energy is used to operate simple resonantcircuits.

[0003] WO 98/36395 describes a method for producing codedradio-frequency signals, in which thermal energy is converted toelectrical energy, and the low-frequency electrical energy is convertedto radio-frequency electrical energy via an element with a nonlinearcharacteristic. This radio-frequency energy is used in order to transmita narrowband radio-frequency signal, which contains specificinformation.

[0004] The data sheet relating to “Funkfernsteuerung Alpha Radio” [RadioRemote Control, Alpha Radio] contains typical operating data for aportable radio remote control.

[0005] The object of the present invention is to provide one option forthermally fed information transmission with low activation energies andan increased information density.

[0006] This object is achieved by means of a thermally fed transmitteras claimed in claim 1, by means of a method as claimed in claim 17, bymeans of an application as claimed in claim 20, and by means of a systemas claimed in claim 22.

[0007] For this purpose, the transmitter has at least one heattransducer element with a downstream voltage transformer. The voltagetransformer ensures that an essentially constant voltage can be tappedoff at least over a short time period. This avoids voltage spikes, andimproves the operational reliability.

[0008] A logic assembly designed on a ULP (Ultra Low Power) basis isconnected to the voltage transformer with the words Ultra Low Power inthis case preferably being understood to mean a power consumption ofless than about 15 mW, and in particular less than 10 mW. A powerconsumption of between 3 mW and 8 mw is particularly advantageous. Thelogic assembly contains at least one sequence controller for controllingthe transmission stage. A data transmission unit is connected to thelogic assembly, and is controlled by it.

[0009] The signals which are produced by the data transmission unit arebroadband signals, in contrast to previous methods, such as thosedescribed in WO 98/36395 or “Funkfernsteuerung Alpha Radio” [RadioRemote Control, Alpha Radio]. This results in the advantage that,although the energy consumption per unit time is higher than in the caseof narrowband transmission, more information can, however, also betransmitted per unit time, so that overall, this allows a higher datatransmission rate and reduced energy consumption. This is particularlyimportant when only small amounts of energy can be used, for exampletemperature gradients.

[0010] It is preferable for at least one heat transducer element to be athermoelectric transducer (thermal transducer). This uses a spatialtemperature difference to produce the voltage. For this purpose, it istypically thermally connected on the one side to a heat-transmittingpart, and on the other side to the environment (possibly via anauxiliary apparatus such as a heat sink KK). The hot and cold sides canalways be interchanged.

[0011] If there is no usable spatial temperature difference in themeasurement environment, it is advantageous for at least one heattransducer element to be a pyroelectric transducer, by means of whichthermal energy can be converted to electrical energy on the basis of thepyroelectric principle, in which a change in temperature over time isconverted to an electrical voltage.

[0012] The energy supply can advantageously be assisted by theadditional use of solar cells. This also allows the transmitter to beoperated when no adequate temperature difference is available, but thereis an adequate light intensity. The particularly low-power design of thetransmitter allows particularly small and cost-effective photovoltaicelements to be used.

[0013] In order to improve the efficiency, it is advantageous for thevoltage transformer to be equipped with a further energy storageelement, preferably an inductance. This is particularly advantageouswhen the voltage transformer circuit is operated on a clocked basis.

[0014] A voltage transformer with a high efficiency and a wide inputvoltage dynamic range is preferably used, according to the prior art,for voltage stabilization. If the charge voltage across the capacitorthen falls during operation from, for example, 20 V to 5 V, astabilization circuit produces a constant 3 V at the output.

[0015] For power-saving operation, the logic assembly is advantageouslydesigned such that all the functions are operated for as short a time aspossible (energy management), in particular in the range ofmilliseconds, especially for an activation duration between 0.3 ms and 5ms, and preferably between 0.5 ms and 2 ms.

[0016] In order to improve the data protection, it is advantageous forthe logic assembly to be connected to a memory in which anidentification code is stored. By way of example, this memory may beintegrated in the logic assembly.

[0017] For reliable operation of the logic assembly, it is alsoadvantageous for it to have at least one rectifier circuit connectedupstream of it. The rectifier and the voltage transformer may beconnected directly or via an additional electrical energy storageelement, for example a capacitor or a rechargeable battery with anassociated circuit. Since the currents that are generated are verysmall, a circuit which saves an extremely large amount of current isrequired. (See invention application, Thermal voltage generator). When acapacitor is used, for example, a downstream voltage transformer canconvert a typically exponentially decaying charge voltage on thecapacitor to a voltage which is constant at least for a short time.

[0018] The heat transducer element may also itself store the electricalvoltages. The electrical energy storage element ensures that an energysupply is available for a sufficiently long time to send theinformation.

[0019] If an adequate voltage signal is available for supplying energyto the logic assembly, then the logic assembly transmits data, forexample an identification code and sensor measurement signals, to thedata transmission unit, which generates a transmission messagecontaining the data to be transmitted, and transmits this over a broadbandwidth.

[0020] It is preferable for the logic assembly to be connected to atleast one sensor. Measurement data from the at least one sensor can thenbe recorded and read by the logic assembly applied to the transmissionmessage, interrogating one or more sensors. There is no restriction tothe choice of sensors; for example temperature sensors, force sensors(pressure, weight, torque, etc.), count sensors or switch state sensorsmay be connected. The measurement data may also, however, be processedin a different manner, for example being digitized, in the logicassembly.

[0021] It is advantageous for the logic assembly to contain amicroprocessor or an ASIC module.

[0022] Some of the electrical energy which is produced by the heattransducer element is typically used to raise the logic assembly to anoperating state. An oscillating crystal is normally provided as a clocktransmitter for this purpose. In order to shorten the time for startingup the logic assembly, it is advantageous for the clock transmitter tobe an LC resonant circuit or an RC resonant circuit rather than anoscillating crystal.

[0023] In order to achieve a high data transmission rate, it isadvantageous for the data transmission device to transmit a signal at afrequency of f>1 MHz. By way of example, frequencies f of between 100MHz and 30 GHz are now technically feasible. Advantageous frequencyranges are bands at 433 MHz, 868 MHz, 2450 MHz (+915) and/or at 5.8 GHzat 24 GHz. There is no fundamental upper limit to the frequency.

[0024] In order to achieve a high data throughput rate within a shorttime, it is advantageous for the bandwidth of the transmitted signal tobe at least 100 kHz, and in particular between 300 kHz and 600 kHz. Thenet amount of data transmitted is preferably 32 bits to 512 bits.

[0025] A transmission time of less than 3 ms, and in particular between0.5 ms and 2 ms, is likewise advantageous.

[0026] The data transmission unit preferably operates with an SAWresonator as the frequency-determining component.

[0027] An error-tolerant transmission method is preferred, in particularusing the so-called forward error correction or a block-orientedredundancy method.

[0028] It is likewise advantageous to transmit the data in a very shorttime for collision protection when two or more transmitters are presentin the reception area of the evaluation electronics.

[0029] If a sufficiently long-term voltage supply is available, it isadvantageous for two or more transmission messages to be transmittedcompletely more than once successively, since this achieves bettertransmission reliability.

[0030] In order to improve the protection against eavesdropping, it isadvantageous for the transmission message to be scrambled, typically bymeans of scrambling logic which is integrated in the logic assembly.This also makes it possible to improve the transmission reliability byentering individual keys, for example for access control. In particular,when transmitting two or more transmission messages, it is advantageousfor each of the radio-frequency signals to be scrambled differently, forexample using a different key.

[0031] In order to suppress transmission interference, it is alsoadvantageous when transmitting two or more transmission messages to varythe time interval between them and/or to use different frequencies forthem.

[0032] In order to improve transmission reliability once again, inparticular in environments where there are two or more transmitters, itis advantageous for the transmission of the transmission message to bedelayed in time, for example by means of a variable, for example random,setting of a delay. The delay can be produced, for example, in the logicassembly software.

[0033] It is preferable for the logic assembly, during one transmissioncycle, at least

[0034] to read the identification code, for example from a memory in thelogic assembly;

[0035] to generate a transmission message which contains at least theidentification code and, possibly, other information such as measurementdata from sensors;

[0036] to activate the data transmission unit and to transmit thetransmission message, possibly scrambled and/or delayed in time, via it.

[0037] The transmitter which can be fed thermally can advantageously beused, inter alia, in:

[0038] temperature sensors for heat cost distribution;

[0039] temperature sensors for domestic purposes, in particular incookers, ovens, refrigerators, domestic appliances;

[0040] sensors in an automobile and in other vehicles;

[0041] temperature sensors and other thermally operated sensors onmachines, systems, vehicles etc. in industry.

[0042] It can also advantageously be used in building technology, inparticular for installation engineering, for example for controllingelectrical systems or for access control.

[0043] The list of applications is not complete; in fact, thetransmitter can be used universally.

[0044] Individual aspects of the transmitter will be explained in moredetail in the following text. The transmitter is not, of course,restricted to these examples.

[0045] a) Energy Analysis

[0046] The electrical energy in a bending transducer is assumed to be:E=½ C·U²=½50·10⁻⁹·50² [V² As/V]=62.5 μWs, leaving approximately 50 uWsassuming that the transducer efficiency is 80%. An electronic circuitwhich, for example, requires about 20 mW (3 V and 6.6 mA) can thus beoperated for a time period of t=50 μWs/20 mW=2.5 ms. The logic assemblyand the data transmission unit can thus be operated for a short timewith little energy as well.

[0047] b) Data Transmission

[0048] i) Transmission Rate and Amount of Data

[0049] Assuming that a data transmission unit in the form of aradio-frequency transmitter is modulated at a rate of 100 Kbit/s, then atotal amount of about 250 bits of data can be transmitted in this time.This amount of data is sufficient for scrambling, and also offers thecapability to increase the transmission reliability by repeatedtransmission or by the use of correlation methods.

[0050] c) Data Transmission Unit

[0051] A power of 1 mW to 50 mW is basically required to transmit datareliably to any point within a private dwelling (when using aradio-frequency transmitter). In this case, one typical scenario is forthe transmission messages from all the transmitters to be received by asingle receiver which initiates the appropriate actions (for exampleheating control).

[0052] d) Receiving System

[0053] The receiving system typically has one receiver and oneprocessor-based signal processing unit. The system receives thetransmission messages which are transmitted from the transmitter, andthese are temporarily stored and processed. The receiving system can becoupled to one or more transmitters to form a system.

[0054] The receiving system is preferably connected to or integrated ina power line communication (PLC) modem see, for example, the SüddeutscheZeitung [South-German Daily Newspaper] dated Mar. 29, 2001, No. 74, page27. A transmission message which is transmitted by the transmitters canbe introduced to a PLC network by means of the PLC modem. This allows acontrol system to be formed which can be remotely controlled by means ofPLC technology, for example for remote diagnosis, maintenance andcontrol.

[0055] The method of operation of the thermally fed transmitter isillustrated schematically in the following exemplary embodiments.

[0056]FIG. 1 shows various functional units of a thermally fedtransmitter,

[0057]FIG. 2 shows a receiving unit,

[0058]FIG. 3 shows a temperature sensor using the transmitter which canbe fed thermally, and

[0059]FIG. 4 shows an apparatus for monitoring a bearing temperature.

[0060] In FIG. 1, first of all charge separation and hence a voltage areproduced by supplying thermal energy in the heat transducer element 1,preferably a thermoelectric or pyroelectric transducer.

[0061] This voltage is used, via a rectifier circuit 2, to charge anelectrical energy storage element in the form of a capacitor 7 orrechargeable battery. The voltage transformer 3 can likewise also be feddirectly, with the heat transducer element 1 itself, for example,storing the charges. The subsequent voltage conversion is advantageousin order to produce a constant voltage over a short time period from theexponentially decaying charge voltage across the capacitor 7.

[0062] The output voltage from the voltage transformer 3 is used toactivate the downstream logic assembly 4 and the data transmission unit(in this case: the radio-frequency transmission stage 5) and to supplythem for as long as the stored energy allows.

[0063] The logic assembly 4 contains a microprocessor sequencecontroller, a memory in which the identity of the transmitter is storedand, optionally, sensor inputs via which the measurement values from oneor more connected sensors 8 can be read in.

[0064] The radio-frequency transmission stage 5 produces aradio-frequency oscillation which is transmitted over a broad bandwidthvia a transmission antenna 6. The transmission message produced by thelogic assembly 4 is modulated onto this oscillation.

[0065] If a sufficient amount of energy is available, then the followingprocessor-controlled sequence is initiated, inter alia, in thisexemplary embodiment:

[0066] a) the identification code is read;

[0067] b) measurement data is read from the connected sensors 8, withthe measurement values being digitized and/or preprocessed;

[0068] c) the data is scrambled;

[0069] d) a transmission message is generated, containing at least theidentification code and the measurement data from the sensors 8;

[0070] e) the radio-frequency transmission stage 5 is activated andcontrolled;

[0071] f) the radio-frequency oscillation is modulated with thetransmission message (possibly more than once, as long as sufficientenergy is available or until some other termination criterion isreached).

[0072] Further steps may, of course, also be provided. In addition, thesteps may be carried out in a different time sequence, for example thesteps a) and b) and/or d) and e) may be interchanged or carried out atthe same time.

[0073] As an alternative to the transmission of radio-frequency signals,other types of data transmission may also be used, for example opticaltransmitters, Bluetooth, etc.

[0074]FIG. 3 shows an apparatus for monitoring a cooking process.

[0075] Cooking processes for foodstuffs in large kitchens, bakeries andin the private domestic environment require a high degree of care andcontinuous readjustment of the heating power and other parameters. Thecooking process can be monitored by monitoring the temperature and otherparameters. The cooking process can thus be controlled optimally, andwith energy being saved, with less care.

[0076] Until now, programs which run automatically once they have beenstarted have been used for this purpose. However, these have theweakness that the weight and condition of all the constituents and ofthe cooking containers must be determined and taken into account inadvance. Closed-loop control is impossible. Solutions are likewise knownin which the temperature of the item to be cooked is determined by meansof plug-in wire-connected sensors (the connecting cable is adisadvantage) or by means of the external temperature of cookingcontainers by measuring the thermal radiation (this has the disadvantagethat the temperature of the item to be cooked is measured indirectly andthis is feasible only with specially coated saucepans, etc.). Despitethe stated disadvantages, these do in fact allow closed-loop control ofthe cooking process.

[0077] The monitoring apparatus described in this exemplary embodimentcomprises the transmitter which has been described above can be fedthermally, and can determine the relevant data in the item to be cookedor in the cooking container and can then transmit this data, for exampleby radio. The data can then be passed to a control device which thusprovides closed-loop control for the heating process. An automaticsystem such as this for closed-loop control of cooking process may, ofcourse, also control two or more cooking processes at the same time.

[0078] The monitoring apparatus is designed such that it operates at thetemperatures which occur during the cooking process. The thermal energywhich is available in the cooking container or in the item to be cookedis used for operation of the monitoring apparatus.

[0079] The monitoring apparatus is highly flexible and can be used inparticular without the need for special cooking containers, since it canbe introduced directly into existing saucepans, etc. or into the item tobe cooked. The transmission antenna 6 is in the form of a thin wirewhich, in the case of metal saucepans, projects slightly out of theclosed lid. The monitoring apparatus is encapsulated such that it isdishwasher resistant, and can be handled like normal cooking equipment.

[0080] In addition to this universally usable variant, it is alsopossible to fit the monitoring apparatus permanently in a cookingcontainer. This is preferably done at positions in which the thermalload of the electronics is kept within limits, and which at the sametime provide an adequate thermal gradient. Particularly in the case ofpermanent installation, sensors 8 for the detection of moisture, fillinglevels and conductance values may also be provided in addition to a puretemperature sensor system.

[0081] The receiving system receives the transmission messagestransmitted from the sensor for the item to be cooked, controls thecooking process (for example by adjusting the temperature of thehotplate), and/or indicates it (for example the remaining cooking time).

[0082]FIG. 4 shows a side view of an apparatus for monitoring a bearingtemperature.

[0083] Temperature monitoring is required in many different fields ofapplication in order to monitor an operating capability and, in theevent of an excessively high or excessively low temperature, to initiatean appropriate reaction in order, for example, to allow preventativesystem maintenance or diagnosis of the wear profile or the like.

[0084] If the part to be monitored is equipped with a temperature sensorwhich is connected via a cable to a central signal processing facility,this results in considerable complexity for cable laying and its design.Furthermore, it would then not be possible to monitor many parts of thesystem (or monitoring would be possible only with a high degree ofcomplexity) since a cable connection is impossible, or is moredifficult, since they move.

[0085] In this exemplary embodiment, the bearing temperature ismonitored by fitting the apparatus to a shaft W via a shaft bearing WLin which a transmitter S which can be fed thermally is provided, havingat least one sensor 8 in the form of a temperature sensor. Thetemperature sensor may be fitted to or in the shaft bearing WL, and thedata is transmitted via radio. The proposed solution can be constructedsuch that it is very compact, and requires no connecting cableswhatsoever and no maintenance. Since no parts subject to wear (forexample batteries) need be maintained, the housing of the entirearrangement can be hermetically sealed, thus also improving thereliability. Finally, no cable laying is required for the installation,and all that is necessary is to inform the system controller that a newtemperature monitoring point has been installed.

[0086] In this exemplary embodiment, the heat transducer element 1 is athermal transducer, in which, preferably, one of its ends is connectedto the system part to be monitored while its other end is connected to apoint which is relatively cool (for example in the event of thetemperature of the system part to be monitored being excessive). This istypically a heat sink or the housing. Since the voltages that areproduced are relatively small, the thermal transducer advantageouslycomprises a series circuit and/or a parallel circuit formed by a largenumber of thermoelectric generator elements.

[0087] The logic assembly 4 monitors the measurement value from thetemperature sensor 81 for a (possibly preset) limit value TGRENZ beingexceeded. If the temperature falls below or rises above TGRENZ, then thelogic assembly 4 generates a transmission message and sends it via thedata transmission unit 5, 6 to a system controller, which is equippedwith an appropriate radio receiver 9, 10 for this purpose. Thistransmission message may contain not only the temperature T at themeasurement point but also, for example, an identification code and/oradditional information. Independently of this, the profile of thetemperature T may optionally be permanently stored in the logic assembly4 in order, for example, to be available for diagnosis purposes after asystem defect.

[0088] This may be a single process, or the transmission may be carriedout cyclically for as long as the temperature is above the limit. Inaddition, a message can be transmitted when the temperature reaches orfalls below the limit value or, for example, the transmission messagemay include the time since the temperature exceeded the limit value.Finally, it is also possible to use two or more limit values, forexample for an initial warning, an alarm and for system disconnection.

[0089] In particular, it is advantageous to use at least one sensor 8 inwhich even small amounts of energy can change a measurement value. It isthus possible to detect a state change whose energy transfer is toosmall for operation of the transmitter. The sensor 8 is advantageouslyan accumulating sensor in which a measurement value which is integratedover time is detected by the energy transfer.

[0090] By way of example, a temperature profile may be stored in anonvolatile memory as the sensor 8, with the memory preferably being inthe form of an extremely low-energy EEPROM memory. Analog storagemethods may also be used, for example discharging of at least onecapacitor or vaporization as a result of a temperature influence, thedischarging of electret materials by radioactive radiation (accumulatedradiation load), electrochemical reactions such as hydrolysis, magneticstorage methods, etc. for (generally integrating) storage of temperatureinfluences and other measurement variables.

[0091] As soon as a relatively large amount of energy is then available,for example as a result of a sufficiently steep temperature gradient oras a result of external energy being supplied (for example via aradio-frequency field), the entire temperature history or a part of itor the accumulated measurement value is transmitted by radio.

[0092] In general, it is advantageous for the transmitter to have as adiscrete component or, for example, integrated in the logic assembly amonitoring unit, for example a threshold value switch, which initiatesthe transmission process when a specific adequate amount of energy isexceeded.

1. A transmitter which can be fed thermally having at least one heattransducer element (1) with a downstream voltage transformer (3), alogic assembly (4) which is connected to the voltage transformer (3) andhas sequence control, a data transmission unit (5, 6) which is connectedto the logic assembly (4), characterized in that the logic assembly (4)is designed on a ULP basis, and the data transmission unit (5, 6)transmits a broadband signal.
 2. The transmitter as claimed in claim 1,in which the logic assembly (4) designed on a ULP basis has a powerconsumption of less than 10 mW.
 3. The transmitter as claimed in one ofclaims 1 or 2, in which the bandwidth of the broadband signal is morethan 100 kHz, in particular between 300 kHz and 600 kHz.
 4. Thetransmitter as claimed in one of the preceding claims, in which thelogic assembly (4) has an LC resonant circuit or an RC resonant circuitas a clock transmitter.
 5. The transmitter as claimed in one of thepreceding claims, in which at least one heat transducer element (1) is athermal transducer by means of which thermal energy can be converted toelectrical energy on the basis of the thermoelectric principle.
 6. Thetransmitter as claimed in one of the preceding claims, in which at leastone heat transducer element (1) is a pyroelectric transducer, by meansof which thermal energy can be converted to electrical energy on thebasis of the pyroelectric principle.
 7. The transmitter as claimed inone of the preceding claims, in which the heat transducer element (1) isfollowed by a rectifier circuit (2).
 8. The transmitter as claimed inone of the preceding claims, in which a solar cell is provided as anadditional electrical power supply.
 9. The transmitter as claimed in oneof the preceding claims, in which the electrical energy which is emittedfrom the heat transducer element (1) can be stored in at least oneelectrical energy storage element, in particular a capacitor (7) or arechargeable battery.
 10. The transmitter as claimed in one of thepreceding claims, in which the voltage transformer circuit (3) can beoperated on a clocked basis.
 11. The transmitter as claimed in one ofthe preceding claims, in which the data transmission unit (5, 6) has anSAW resonator as the frequency-determining component.
 12. Thetransmitter as claimed in one of the preceding claims, in which thelogic assembly (4) is connected to at least one sensor (8).
 13. Thetransmitter as claimed in claim 12, in which the at least one sensor (8)is an accumulating sensor.
 14. The transmitter as claimed in one of thepreceding claims, in which the transmission stage (5) is aradio-frequency transmission stage, by means of which a radio-frequencysignal at a frequency (f) of more than 1 MHz, in particular at afrequency (f) of between 100 MHz and 30 GHz, can be transmitted.
 15. Thetransmitter as claimed in one of the preceding claims, in which a delayapparatus is provided between the logic assembly (4) and a transmissionantenna (6) of the data transmission unit (5, 6).
 16. The transmitter asclaimed in one of the preceding claims, in which the logic assembly (4)is connected to memory, in which an identification code is stored.
 17. Amethod for operation of a transmitter as claimed in one of the precedingclaims, in which a transmission message is transmitted within a timeperiod of 0.3 ms to 5 ms, in particular between 0.5 ms and 2 ms.
 18. Themethod as claimed in claim 17, in which two or more transmissionmessages are transmitted successively.
 19. The method as claimed inclaim 18, in which a time interval and/or the frequency (f) of thetransmission messages can be adjusted variably with respect to oneanother.
 20. The method as claimed in one of claims 16 to 19, in whichthe information in the transmission message is scrambled, in particularif two or more transmission messages are scrambled differently.
 21. Useof a transmitter as claimed in one of claims 1 to 15 for heating, forcooking or for system engineering.
 22. A system for monitoring and/orcontrol, having at least one transmitter as claimed in one of claims 1to 15, at least one unit for indication of data which is transmittedfrom the at least one transmitter and/or for controlling at least one ofthe apparatus which are monitored by the transmitter, on the basis ofthe received data.
 23. The system as claimed in claim 22, fortemperature monitoring, in particular for cooking area monitoring orsystem monitoring.